Process for producing finely divided metal products



March 12, 1968 J, HARDY ET AL PROCESS FOR PRODUCING FINELY DIVIDED METALPRODUCTS Filed Nov. 6, 1964 INVENTOR. J. E HARDY, M. E. JORDAN UnitedStates Patent Ofiice 3,373,013 Patented Mar. 12, 1968 Walpole, Boston,Mass.,

This invention relates to a process for producing metallurgicalmaterials. More precisely, the invention disclosed herein relates to animproved process for producing finely divided metallurgical powders ofsubmicron dimensions.

Finely divided metallurgical powders including metal, metal oxide andmetal carbide powders are well known products of commerce. Such productspresently have many known specialized applications and their potentialapplications are regarded as especially promising. Many processes areknown for producing such metallurgical powders and in general, thefineness and purity of the ultimate powder is primarily determined bythe process utilized. For example, the most finely divided and purestpowders are produced by elaborate and highly specialized ball millingtechniques and also by vaporization or fuming techniques. Accordingly,the said powders are rather expensive because of the intricate processesinvolved in producing them. In view of the growing need for high puritymetallurgical powders and especially those having average particlediameters below about one micron, any process whereby such powders canbe produced consistently, easily and in a simple and inexpensive fashionwould be indeed 'a notable contribution to the art.

A principal object of the present invention is to provide an improvedprocess for making the foregoing contribution to the art.

A more specific object of the present invention is to produce finelydivided metallurgical powders especially metal oxide powders in anextremely economical fashion.

Still another object of the present invention is to provide a simpleprocess for producing powdered metals, or metal carbides in a finelydivided form.

Another object of the present invention is to provide a process forproducing powdered metals, metal oxides or metal carbides in a finelydivided form in combination with varying amounts of carbon whichcombinations have specialized properties and are of particular utility'as fillers and/or as pigments in elastomeric and plastomericcompositions.

Other objects and advantages of the present invention will in part beobvious to those well skilled in the art or will in part appearhereinafter.

In a very broad sense, the above-mentioned objects and advantages arerealized in accordance with the practice of our invention by subdividinga slurry containing carbon black and at least one metal compound andintroducing said subdivided slurry to a fluidized bed of solid materialsmaintained at a temperature sufliciently elevated to convert saidcompound to at least the corresponding oxide. Thus, the principles ofour invention reside not only in the ingredients and the form thereofutilized but also in the specific manner of subsequently converting saidcompound in a surprisingly easy fashion to a metallurgical powder.

The operational features of the present invention will be betterunderstood by reference to the attached drawing. Said drawingillustrates a view in elevation of an arrangement of apparatus withportions of said appa= ratus cut away to illustrate features thereof inmore detail.

Referring now to the attached drawing, carbon black, preferably inslurry form, is fed to mixer 14 via line 16 while a slurry or solutionof the metal compound(s) is fed to mixer 14 via line =12. Mixer 14 isprovided with suitable agitation means (not shown) to produce anintimate mixture in slurry form of the carbon black 1 and metalcompound. Said slurry is then conveyed preferably at a controlled rateand in any convenient manner, such as with the aid of gas from reservoir20, from mixer 14 by way of line 16 to reactor 28. The terminal portionof line 16 should preferably be equipped with a fine spray nozzle 24 sothat the slurry of black and metal compound is subdivided and introducedin aerosol form to reactor 28.

Reactor 28 is an enclosed, usually cylindrical, heated vertical chamber.Means for heating said chamber are not shown since many manners obviousto those skilled in the art of heating reactor 28 directly or indirectlyare suitable for the practice of our invention. The major portion of theinterior of reactor 28 is occupied by a plurality of heated particulatebodies 26 which are maintained in a fluidized state preferably by thegas from reservoir 20. In this respect, it is to be understood thatauxiliary gas can also be introduced to reactor 28 through nozzle 24 orother entry ports to maintain bodies 26 in a fluidized state. It is tobe also understood that the preferred fiuidizing action should normallybe so adjusted as to maintain attrition of bodies 26 at a minimum.

The sub-divided carbon black/metal compound slurry which is sprayed intoreactor 28 contacts heated bodies 26 and is converted to the desiredmetallurgical powder. After conversion, since the powder is considerablysmaller in size than bodies 26, the powder is selectively conveyed bythe fluidizing gas from reactor 28 to suitable collection means 32.

In the most preferred embodiment of our invention, bodies 26 arecomprised of the same material as the metallurgical powder produced inreactor 28. That is to say, when the metal compound is to be convertedin reactor 28 to the corresponding oxide, then bodies 26 should also becomprised of said oxide. This feature assures maximum purity of thepowder produced in accordance with the practice of our invention. Ifpurity is not a paramount consideration, said bodies can be comprised ofany desired refractory and substantially inert material including metal,metal oxide, metal carbide and ceramics. It is to be understood thatsuch features as the size of said bodies, the amount thereof in saidreactor, the rate at which the slurry is introduced to the reactor andthe rate of gas flow through the reactor will vary and be determined byfactors such as the temperature in the ractor, the geometry thereof, themetallurgical powder desired, the particle size of the powder desired,etc. However, suitable operational conditions for any given system canbe readily determined by those well skilled in the art. For example,helpful details on fluidized bed systems can be found in Perrys ChemicalEngineers Handbook, 4th edition, Sections 2042 to 20-53.

We have found that carbon black is an essential ingredient ineifectuating the purposes of our process since even in those cases wherecarbon black is theoretically not required to produce the desiredproduct, for example, in the production of metal oxides, the presencethereof normally permits the conversion of the metal compound to thedesired corresponding metal powder to be achieved much more rapidly orat temperatures much lower than those normally required to accomplishsaid conversion in the absence of carbon black. Also, the use of carbonblack permits one to conveniently apply the practice of our invention tothe direct production of diverse metallurgical s powders since theamount of carbon black utilized can be selectively adjusted to conformto the stoichiometrtc amount required to directly convert the metalcompound to such finely-divided metallurgical powders including powderedmetal oxides, carbides and metals.

For the purposes of the present specification and the claims attachedhereto, carbon black refers generally to products produced by thecatalytic cracking and/or incomplete combustion of hydrocarbonaceousmaterials. Thus, for example, materials referred to in the art asacetylene blacks, lamp blacks, channel blacks, furnace blacks, thermalblacks, etc., are all included within the scope of the presentinvention.

Broadly, the metal compounds utilized in the practice of our inventioninclude compounds of metals such as boron, silicon, barium, copper,aluminum, titanium, zirconium, tungsten, zinc, lead, tin, iron, cobalt,nickel, manganese, chromium, vanadium, thorium, molybdenum and mixturesof these. More specifically, however, the present invention relates tometal compounds which can be thermally decomposed or converted undersuitable conditions to produce the corresponding metal, metal oxide ormetal carbide. Representative preferred compounds include the sulfates,chlorides, bromides, iodides, fluorides, perchlorates, orthoarsenates,sulfides, acetates, citrates, oxalates, formates, benzoates, carbonates,oleates and tartrates of the above-mentioned metals. Especiallypreferred are the water soluble organic and inorganic compounds of theabove-mentioned metals. The benefits which flow from the practice of ourinvention are especially apparent when compounds of the above-mentionedmetals which can be converted to the desired metal powder attemperatures above about 500 F. but below about 2500 F. are utilized.Thus, such compounds constitute an especially preferred embodiment ofour invention.

The exact amount of carbon black to be combined with any of theabove-mentioned compounds will be determined primarily by the finalmetal powder desired. As stated, the practice of our invention can beapplied to the production of diverse metallurgical powders. Such powdersinclude powdered metals, metal oxides, metal carbides, mixtures of metaloxides, metal/metal oxide mixtures and metal/metal carbide mixtures.However, it is tobe understood that the practice of our invention doesnot necessarily require that any of the aforesaid powders except themetal oxides be produced directly. In other words, the practice of ourinvention is satisfied by merely converting metal compounds to thecorresponding oxides. Said oxides can then be treated in any desiredfashion to convert said oxides to the corresponding free metal orcarbide or mixtures thereof.

The minimum amount of carbon black to be combined with the aforesaidcompounds can readily be determined in practice. While some variationswill occur, amounts of carbon black set forth in our copending US.Patent application 375,942 filed June 17, 1964, are generally entirelysuitable for the practice of the present invention. When the practice ofour invention is applied to the direct production of powdered metals,metal carbides, metal/metal oxide mixtures and metal/ metal carbidemixtures, the, minimum amount of carbon involved will normally be aboutequivalent to the stoichiometric amount requiredto produce the desiredpowder.

The amount of residual carbon black which can be tolerated incombination with the final metallurgical pow der is another factor whichcan affect the amount of carbon black to be combined with the aforesaidcompounds. We consider our process most valuable when applied to theproduction of finely-divided metallurgical powders of high purity, thatis to say, metallurgical powders in combination with very smallquantities of carbon black, i.e. less than carbon black by weight of thetotal composition. Accordingly, in the most preferred embodiment, theamount of carbon black utilized will rarely exceed the amount requiredto produce compositions comprising about 10% by weight carbon black.

However, it is to be understood that our process can also be applied tothe production of finely-divided metallurgical products in combinationwith larger amounts of carbon black. Such compositions can be utilizedas fillers in elastomeric or plastorneric compositions and accordingly,can contain up to about 90% by weight of carbon black if desired. I

The temperature at which the metal compound in the carbon black/metalcompound mixture can be converted to form the desired metallurgicalproduct can vary over a wide range. In general, the range includestemperatures substantially below those normally required to convert the,metal compound as well as temperatures that can exceed said normaldecomposition temperature by 400 or 500 F. and even more. Since ourprocess is operated continuously, it is obviously normally desirable toreduce residence time to a minimum and thus the temperature of the convension zone will be relatively high.

The environment in the conversion zone will also be determined primarilyby the final metallurgical product desired and said environment caneasily be selected by one well skilled in the art. For example, if theultimate powder is to be a metal oxide of high purity (i.e. low carbonblack content) then an oxidizing environment is definitely preferred.The oxidizing environment not only insures a rapid conversion of themetal compound to the corresponding oxide but also is effective inreducing the residual carbon content in combination with the finalpowder. Furthermore, when the conversion temperature utilized is higherthan that normally required to convert the metal compound in the absenceof any carbon black, and especially when larger amounts of carbon blackare utilized, an oxidizing environment is also definitely preferredsince reduction or carbide-forming reactions are thereby inhibited. Aninert environment is often suitable for the production of metal oxideswhen the conversion temperature is closely controlled and maintainedbelow or at about the temperature at which the compound normallydecomposes to form the oxide unless, of course, the metal compound isone which cannot be decomposed to form the oxide in the absence of anoxidizing environment.

A reducing or inert environment is definitely preferred when thepractice of our invention is applied to the direct production ofpowdered metals, metal/metal oxide mixtures and metal/metal carbidemixtures. Inert and reducing environments are also usually preferredwhen carbides are produced in accordance with our invention.

The following specific examples of particular embodiments of ourinvention are given for the purposes of providing a fuller and morecomplete understanding of some of the operating details of the inventiontogether with many of the advantages to be obtained from practicingsame. These examples should be considered as illustrative only and as inno sense limiting the scope of the present invention.

Example 1 In apparatus of the type set forth in the attached drawing, aslurry was prepared by mixing an, aqueous dispersion of carbon black andan aqueous solution of nickel sulfate. The concentrations of carbonblack and nickel sulfate were adjusted so that the weight of carbonblack in the final slurry represented 5% by weight of the total solids.Said slurry was then entrained in air under a pressure of about lbs/sq.in. and was continuously conveyed at a rate of about 10 lbs/hr. to anexternally heated vertical chamber containing 20 lbs. fluidized nickeloxide pellets having an average particle diameter of about 500 microns.The average temperature of the fluidized mass was maintained at about1500 F. The settled depth of the mass of nickel oxide pellets making upthe bed was about 2 feet, the average velocity of the gas through saidbed being about 5 ft./second. A finely-- divided composition comprisingcarbon black and nickel oxide was continuously collected in a cyclonecommunieating with the upper discharge end of said chamber.

lectron microscope examination of said composition revealed that theparticle size of substantially all of said composition was in the submicron particle range.

Example 2 In the same apparatus utilized in Example 1, a slurry wasprepared by mixing an aqueous dispersion of carbon black and an aqueoussolution of titanium sulfate. The concentrations of carbon black andtitanium sulfate were adjusted so that the weight of carbon black in thefinal slurr represented 5% by weight of the total solids. Said Slurrywas then entrained in air under a pressure of about 50 lbs/sq. in. andwas continuously conveyed at a rate of about lbs/hr. to an externallyheated vertical chamber containing about lbs. of fluidized titaniumdioxide particles having an average particle diameter of about 300microns. The average temperature of the fluidized mass Was maintained atabout 2000 F. The settled bed depth of the mass of titanium dioxideparticles was about 1.5 ft, average velocity of the gas through said bedbeing about 7 ft./second. A finely-divided composition comprising carbonblack and titanium dioxide was collected in a cyclone communicating withthe upper discharge end of said chamber.

Example 3 In the same apparatus utilized in Example 1, a slurry wasprepared by mixing an aqueous dispersion of carbon black and an aqueoussolution of iron sulfate. The concentrations of carbon black and nickelsulfate were adjusted so that the weight of carbon black in the finalslurry represented about 10% by weight of the total solids therein. Saidslurry was then entrained in carbon monoxide under a pressure of about50 lbs/sq. in. and was conveyed to an externally heated vertical chambercontaining lbs. of fluidized iron shot having an average particlediameter of about 500 microns. The average temperature of the fluidizedmass was maintained at about l800 F. The average velocity of the gasthrough said bed was about 6 ft./second. A finely-divided compositioncomprising carbon black and iron metal was continuously collected in acyclone communicating with the upper discharge end of said chamber.

Example 4 In the same apparatus utilized in Example 1, a slurry wasprepared by mixing an aqueous dispersion of carbon black and an aqueoussolution of ammonium paratungstate. The concentrations of carbon blackand ammonium paratungstate were adjusted so that the weight of carbonblack in the final slurry represented about by weight of the totalsolids therein. Said slurry was then entrained in argon gas under apressure of about 50 lbs/sq. in. and was conveyed to an externallyheated vertical chamber containing 50 lbs. of fluidized tungsten metalpowder having an average particle diameter of about 250 microns. Theaverage temperature of the fluidized mass was maintained at about 2200F. The average velocity of the gas through said bed was about 15ft./second. A finely-divided composition comprising carbon black andtungsten carbide was continuously collected in a cyclone communicatingwith the upper discharge end of said chamber.

It will be obvious from the preceding examples that the process of ourinvention is highly versatile and can be applied to the production ofmany finely-divided metal powders of commercial interest. Thus, manymodifications in many of the incidental features utilized inillustrating our invention can be made without departing from the spiritand scope thereof. For example, while our discussion above has beenlimited to the term slurry, for the purposes of the presentspecification and the claims appended hereto, the term slurry includeswithin its scope the term dispersion.

Also, it is obvious that, if desired, flue gases, for example, fromcarbon black-producing units can be utilized in place of the fluidizingand/or entrainment media utilized above.

Having described our invention together with preferred embodimentsthereof, what we declare as new and desire to secure by US. LettersPatent is as follows:

1. A process for producing finely-divided metallurgical powderscomprising the steps of:

(a) uniformly mixing into a liquid medium (1) at least one metalcompound which upon heating in an oxidizing atmosphere can be convertedto the corresponding oxide, and

(2) carbon black,

(b) subdividing the resulting mixture into droplets and contacting saiddroplets with a plurality of fluidized particulate bodies heated to atemperature at least sufiicient to convert said metal compound to thecorresponding oxide.

2. The process of claim 1 wherein said metal compound is chosen from thegroup consisting of compounds of boron, silicon, copper, barium,aluminum, titanium, zirconium, tungsten, zinc, lead, tin, iron, cobalt,nickel, manganese, chromium, vanadium, thorium, molybdemum and mixturesthereof.

3. The process of claim 1 wherein said metal pound is a compound ofiron.

4. The process of claim 1 wherein said metal pound is a compound ofnickel.

5. The process of claim 1 wherein said metal pound is a compound oftungsten.

6. The process of claim 1 wherein said metal pound is a compound oftitanium.

7. The process of claim 1 wherein said metal pound is a compound ofaluminum.

8. The process of claim 1 wherein said metal compound is soluble in saidliquid medium.

9. The process of claim 1 wherein step (b) is accomplished in anoxidixing atmosphere.

10. The process of claim 1 wherein step (b) is accomplished in an inertatmosphere.

11. The process of claim 1 wherein step (b) is accomplished in areducing atmosphere.

12. The process of claim 1 wherein step (b) is accomplished underoxidizing conditions such that the final product is substantially freeof carbon black.

13. The process of claim 1 wherein the quantity of carbon black utilizedis such that the resulting powder comprises less than about 10% byweight carbon black.

14. The process of claim 1 wherein step (b) is accomplished attemperatures between about 500 F. and about 2500 F.

15. The process of claim 1 wherein said particulate bodies comprise thesame material to which said metal compound is converted.

16. The process of claim 1 wherein said metal compound is chosen fromthe group consisting of sulfates, nitrates, acetates and chlorides.

17. The process of claim 1 wherein a mixture of metal compounds isutilized.

18. The process of claim 1 wherein a metal oxide is produced.

19. The process of claim 1 wherein a free metal is produced.

20. The process of claim 1 wherein a metal carbide is produced.

com-

COIII- com- References Cited UNITED STATES PATENTS 1,984,380 12/1934Odell 134-60 2,242,759 5/ 1941 Schlect et al. 7584 2,288,613 7/1942 Dill7589 2,900,244 8/1959 Bradstreet et a1 75.5 3,305,349 2/1967 Bovarnicket al 750.5

DAVID L. RECK, Primary Examiner. W. STALLARD, Assistant Examiner.

1. A PROCESS OF PRODUCING FINELY-DIVIDED METALLURGICAL POWDERSCOMPRISING THE STEPS OF: (A) UNIFORMLY MIXING INTO A LIQUID MEDIUM (1)AT LEAST ONE METAL COMPOUND WHICH UPON HEATING IN AN OXIDIZINGATMOSPHERE CAN BE CONVERTED TO THE CORRESPONDING OXIDE, AND (2) CARBONBLACK,